1. Field of the Invention
The present invention relates to a process for producing fluoropolymer particles.
2. Discussion of Background
A fluoropolymer has various excellent properties and is thus used in a wide range of applications. For example, a perfluorocarbon polymer having a sulfonic acid type functional group is used for e.g. diaphragms (for alkali electrolysis, electrodialysis, various organic electrolytic syntheses, etc.), polymer electrolyte membranes (for fuel cells, ozone-generating electrolysis, water electrolysis, etc.), polymer catalysts (for organic syntheses, polymerization, etc.) and other membrane materials (for dehumidifiers, humidifying devices, etc.).
In the past, a perfluorocarbon polymer having a sulfonic acid type functional group was produced by a solution polymerization method in a chlorofluorocarbon (such as trichlorotrifluoroethane). Further, also when such a polymer is flocculated from the solution obtained by the solution polymerization method to obtain polymer particles, a chlorofluorocarbon (such as trichlorofluoromethane) was used as a solvent for the flocculation.
However, in recent years, use of a chlorofluorocarbon has been restricted, and a shift to the following substitute solvents has been proposed.
(1) A method for producing a perfluorocarbon polymer having a sulfonic acid type functional group, wherein a specific hydrochlorofluorocarbon, hydrofluorocarbon or fluorocarbon is used as a solvent to be used for the solution polymerization, and a hydrofluoroether compound is used as a solvent for the flocculation (Patent Document 1).
(2) A method for producing fluoropolymer particles, wherein a specific hydrofluoroalkyl ether is used as a solvent for the polymerization, and water is used as a solvent for the flocculation (Patent Document 2).
However, in a case where by the method (1), a hydrofluoroether compound is employed to flocculate the polymer thereby to obtain polymer particles, fine particles will be formed in a large amount, whereby separation of the polymer particles by filtration and recovery of an unreacted monomer tend to be difficult.
Further, also by the method (2), fine particles will be formed in a large amount, separation of such polymer particles by filtration and recovery of an unreacted monomer tend to be difficult.
Patent Document 1: Japanese Patent No. 3,791,137
Patent Document 2: Japanese Patent No. 4,144,463